1. Field of the Invention
The invention relates in general to measuring devices or transducers, and more specifically to transducers for measuring active power or watts, and reactive power or vars, of an alternating current circuit.
2. Description of the Prior Art
U.S. Pat. No. 4,027,241, which is assigned to the same assignee as the present application, and which has now been dedicated to the public, discloses a watt transducer based upon the pulse width-pulse height multiplication principle. A pulse width modulated signal responsive to the instantaneous value of the circuit voltage is used to reverse the output terminals of a current transformer which measures the circuit current. Thus, a train of pulses of alternating polarity is produced, with their height being proportional to the instantaneous measured current, and their width being proportional to the instantaneous measured potential. The average value of the current pulses is proportional to power. The train of current pulses is filtered and applied to a constant current output amplifier, which eliminates the need for zero adjustment.
In addition to measuring active power or watts, it is often desirable to measure reactive power or vars, especially in unbalanced polyphase circuits. It would be desirable to utilize the time division multiplication principle of the hereinbefore mentioned U.S. Patent, as well as the switched current transformer embodiment set forth in this patent, to simultaneously provide an indication of circuit watts and vars. It would also be desirable to provide these functions while minimizing circuit components and thus power supply requirements.